In response to this need, a number of test kits have been developed to enable onsite identification of group A and other beta-hemolytic streptococci in, for example, an office or clinic setting. One of these test kits was evaluated in the article by Slifkin, M. and Gil, G., "Evaluation of the Culturette Brand Ten-Minute Group A ID Technique," J. Clin. Microbiology, Vol. 20, pp. 12-14, 1984. In this study, the latex reagent kit "Culturette Brand Ten-Minute Group A Strep ID" (Marion Scientific, Division of Marion Laboratories, Inc., Kansas City, Mo.) was evaluated for sensitivity, accuracy and suitability for the direct serogrouping of group A streptococci from throat swabs as compared with standard throat swab cultures.
In the Culturette test, a pharyngeal culture was obtained by rubbing a swab over the patient's throat. The swab was placed in a microtube subsequent to the dropwise addition of two extraction agents to the tube. The swab was then rolled against the wall of the microtube to express liquid from the swab into the microtube. After the swab was incubated for five minutes at room temperature, two drops of a third extraction reagent were added. The swab was rolled and pressed against the microtube and then incubated for an additional ten minutes.
The swab, after having been placed in the microtube and extracted, was briefly rolled--to release extraction fluid from the swab--onto two circular areas of the glass slide provided in the kit. One drop of the latex group A Strep ID kit was next added to one of these circular areas, and one drop of the negative control reagent was added to the other circular area. The slide was then rocked back and forth by hand for two to three minutes and examined for agglutination of the latex particles. A positive control reagent was also available in the kit and was employed on a daily basis to test the activity of the group A detection agent.
This study by Slifkin and Gil, although directed generally to the sensitivity and accuracy of the test kit, also illustrates the inconvenient procedures inherent in liquid-reagent test kits. Reagents are added dropwise, and the practitioner can easily dispense too little or too much of any of four reagents. Moreover, two sequential incubations plus a two or three minute rocking period contribute to an overall procedure which is awkward and time-consuming, not to mention potentially inaccurate in the event of procedural error.
Without doubt, busy practitioners need a test for the onsite identification of beta-hemolytic streptococci which is simple and reliable and yet requires only a few minutes of minimized attention.